Should I stay or should I go? This is a common question people ask themselves in their journey through life, but bacteria are also asking the same question.
Zhaomin Yang, an associate professor in the Department of Biological Sciences in the College of Science at Virginia Tech received a $1 million grant from the National Science Foundation (NSF) to understand how bacteria decide whether to stay and build a biofilm or to initiate motility and move to new territory.
"Bacterial biofilms profoundly impact our lives and society because they can form on so many surfaces," said Yang, an affiliated faculty member of the Fralin Life Sciences Institute. "Most acute infections are caused by free-living bacteria, and most chronic infections are associated with biofilm formation in a host. Part of the reason that chronic infections are difficult to treat is because bacterial pathogens in biofilms are more resistant to antibiotics."
Many may think of bacteria as avid swimmers, with their propeller-like flagella that help them to zoom around in the open ocean, a body of freshwater, or other aqueous environments. But Yang says that this is a misconception for two reasons.
First, the motile state of a bacterium is only temporary. In fact, bacteria spend most of their lives in biofilms, which are sessile, or immobile, structures that are attached to solid surfaces. Biofilms are like bacterial communities, complete with houses and roads that are built using self-made materials. But at times, particularly when conditions worsen, bacteria may choose to uproot and move to a more favorable place to build a new biofilm.
They must make their decision carefully. "The back and forth transitions between sessile and motile states are life and death decisions for bacteria, as a right move leads to future prosperity but a wrong one leads to a perilous journey," said Yang.
Secondly, most bacteria don't even have flagella, and some kinds of bacteria must resort to crawling or gliding on surfaces in order to survive.
"People in the old days were often nomads who lived by moving around all of the time. And then there is this other society where people settle down and create communities. Either you are a nomad or you are living in a settlement. You can think of bacteria just like that," said Yang.
Yang said that the transition between biofilm and motile states has been mostly studied with flagellated bacteria. Researchers know surprisingly very little about how the surface-crawling bacteria make and execute their decision to either stick and settle down or uproot and move to a new place.
There are molecular-level changes that must be made for bacteria to put their final decision into action. To develop a biofilm, bacteria have to first disable their motility apparatuses and motor proteins, then produce the building materials for the biofilm. To move somewhere else, bacteria must stop producing the molecules that allow them to stay in the biofilm, followed by constructing and enabling their motility structures.
Yang is specifically looking at Type IV pili (T4P), hair-like surface structures that are found on bacterial surfaces, to understand their perplexing, almost paradoxical, functions.
He explained, "On one hand, it is a motility apparatus that enables many bacteria to crawl over surfaces by extension and retraction like a grappling hook. On the other, it is an adhesin and regulator that enhances biofilm formation."
It is hypothesized that cyclic di-GMP, a signaling molecule in bacteria, can switch the mutually exclusively functions of T4P in biofilm formation and motility on or off by interacting with the T4P motor protein, PilB. Yang uses genes from Chloracidobacterium thermophilum, a bacterium from Yellowstone National Park, for in vitro studies and the bacterium Myxococcus xanthus for in vivo work.
In order for researchers to get a closer look at these molecular processes, this project needs to use advanced imaging and structural analysis. Yang collaborates with Takyuki Uchihashi at Nagoya University in Japan, an expert in high-speed atomic force microscopy (HS-AFM).
Deborah Kelly, the co-principal investigator of this study, is an expert in cryogenic electron microscopy (cryo-EM) in the Department of Biomedical Engineering at the Pennsylvania State University. Kelly also directs the new Center for Structural Oncology at the Huck Institutes of the Life Sciences.
"Interest in cryo-EM has skyrocketed in recent years. The technique is truly transforming our view of life's processes. We're excited to contribute cryo-EM insights to Dr. Yang's project. Together, we can uncover new details of the tiny microbes that play a significant role in the body. The connection between biofilm formation and disease origin remains a major health risk to modern society. Our work aims to address this unmet need for the biomedical community," said Kelly.
Keane Dye, a third-year Ph.D. student in the Department of Biological Sciences, has some expertise in this area since working on his thesis project in Yang's lab.
"I am looking at how cyclic-di-GMP and adenine nucleotides bind to PilB and how the binding of one impacts the binding of the others. Understanding these interactions is necessary in order to provide a biochemical framework for how PilB might regulate the functions of T4P in motility and in the development of a biofilm," said Dye.
Who would have known that bacteria are a lot like us in terms of our desperate need to create communities and settlements?
Yang thanked Ed Smith, the director of the VT PREP and IMSD programs, for his support. Past work on this project has been supported by three standard NSF research grants and an R01 from the National Institutes of Health to the Yang lab.